This invention relates to vehicle speed controllers. Automatic vehicle speed controllers as manufactured in the past have functioned to maintain a vehicle at a predetermined set speed without any assistance from the operator. Such vehicle speed controllers, which are commonly called "cruise controls", act to automatically decelerate the vehicle when it exceeds the set speed, and to automatically accelerate the vehicle when it falls below the set speed. When the cruise control is turned on, the driver removes his foot from the accelerator and allows the cruise control to make the accelerator adjustments that are necessary to maintain the vehicle at the set speed.
The above-described prior art cruise controller has several serious disadvantages. If the vehicle passes over an icy patch on the road while it is being operated by cruise control, the rear wheels may slip on the ice, but instead of decelerating to break the skid, the cruise controller holds the speed up to the set speed. To assume manual control of the vehicle, it is necessary for the operator to either apply the brakes or to switch the cruise controller off. Since application of the brakes might augment the skid, the operator must turn the cruise control off before the vehicle can be decelerated. However, turning the cruise control off is an unfamiliar motion that takes time. Furthermore, the driver may overlook this step or fumble in an emergency, whereas control of foot pressure on an accelerator is an instinctive reaction when the vehicle is under manual control. With the above in mind, it is highly desirable to provide a vehicle speed controller so constructed to offer both the maintained speed operating mode and one in which the operator's foot remains on the accelerator while the controller is operating so that the vehicle can be decelerated at any time by merely releasing the foot pressure on the accelerator.
Another drawback of prior art cruise controllers is that they are relatively expensive.